1. Field of the Invention
This invention relates to a gear pump (commonly called a gerotor pump) and more particularly to a reversible gerotor pump having a movable eccentric member rotatable in response to the direction of rotation of the rotor.
2. Description of the Prior Art
Gear pumps such as the reversible pump described in U.S. Pat. No. 3,273,501 are commonly used to deliver lubricant to compressors, such as refrigerant compressors in a refrigeration system. As explained in U.S. Pat. No. 3,574,489, orbital gear-sets providing rolling contact between an outer internally-toothed gear which has one more tooth than an inner externally-toothed gear and which mesh with their axes eccentric to one another are commercially available under the generic designation "gerotors". Pumps employing such arrangement for positive displacement of fluid caused by the rolling contact between the meshing teeth are referred to as gerotor pumps.
In such gerotor pumps, inlets and outlets are generally defined in face plates on opposing planar sides of the mating gears, and are, for the most part, diametrically opposed (i.e. 180.degree. out-of-phase). Thus, with the gears rotating in one direction, the pump inlet is adjacent the area where the gears are separating and the outlet is adjacent the area where the gears are meshing. By reversing the direction of the gears the outlet becomes the inlet and the inlet the outlet.
However, in instances where reversibility of the pump is desired but yet is is also necessary that the inlet and outlet do not reverse, the rotor (i.e. the outer, internally-toothed gear) has been disposed in an opening of a rotatable eccentric collar member which can be rotated through a 180.degree. arc to change the orientation of the eccentric axes between the rotor and the internal gear such that, in either direction of rotation, the pump has a common inlet and outlet.
The movement or rotation of the eccentric collar member through the 180.degree. arc has been dependent upon a friction between the drive shaft and a rotatable face plate positively engaging the eccentric collar such as shown in U.S. Pat. No. 3,165,066 or between the outer circular surface of the rotor and the internal cylindrical surface of the eccentric member as disclosed in previously mentioned U.S. Pat. No. 3,273,501. An indexing pin or tab is provided that limits the movement of the eccentric member to 180.degree. whereby continued rotation of the rotor causes continuous friction to maintain the member in the extreme position. However, in either instance, this continuous friction also causes wear between the two parts such that in the first instance the frictionally engaging parts will wear out quite readily whereas in the second instance, over a period of time, the friction between the eccentric member and the stationary face plate covering the rotor will be greater than the friction between the eccentric member and the rotor, in which instance the eccentric member is not always responsive to the rotation of the rotor to change its orientation and the pump does not circulate the lubrication as intended, causing damage to the machinery being lubricated.